Optical properties of apple skin and flesh in the wavelength range from 350nm to 2200nm.
Saeys W1*, Velazco-Roa MA2, Thennadil SN2, Ramon H1, Nikolai BM1
Division of Mechatronics Biostatistics and Sensors, Department of Biosystems, Katholieke
Universiteit Leuven, Belgium.
School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle
Applied Optics, 47 (7), 908-919 (2008).
Abstract Optical measurement of fruit quality is challenging due to the presence of a skin
around the fruit flesh and the multiple scattering by the structured tissues. To gain insight in
the light-tissue interaction, the optical properties of apple skin and flesh tissue are estimated
in the 350-2200 nm range for three cultivars. For this purpose, single integrating sphere
measurements are combined with inverse adding-doubling. The observed absorption
coefficient spectra are dominated by water in the near infrared and by pigments and
chlorophyll in the visible region, whose concentrations are much higher in skin tissue. The
scattering coefficient spectra show the monotonic decrease with increasing wavelength
typical for biological tissues with skin tissue being approximately three times more scattering
than flesh tissue. Comparison to the values from time-resolved spectroscopy reported in
literature showed comparable profiles for the optical properties, but overestimation of the
absorption coefficient values, due to light losses.